Tachykinins in the sensory and peripheral nervous system

Solution conformation of a cyclic neurokinin antagonist: a NMR and molecular dynamics study

The solution structure of a hexapeptide, cyclo (Gln-Trp-Phe-Gly-Leu-Met), which is a selective NK-2 antagonist, has been studied by a combination of two-dimensional nmr and molecular dynamics (MD) techniques. The simulation based on nmr and MD data resulted in the convergence to a family of structures. Free molecular dynamics for 50 ps in the presence of DMSO solvent molecules shows that the structure is energetically stable. One intramolecular hydrogen bond between the amide proton of Gln and the carbonyl oxygen of Gly was revealed. This result is consistent with the results from the measurement of the temperature coefficient of the amide protons. The extent of intermolecular hydrogen bonding between the amide protons of the peptide and DMSO was also revealed by the free MD simulation. The resulting structure of the cyclic peptide contains a variation type I' beta-turn in the Gly-Leu-Met-Gln segment. Comparison of the structure of this peptide with that of other NK-2 antagonist cyclic hexapeptides was made, and the activity of cyclic antagonists appears to be inversely related to the conformational rigidity of the cyclic peptides.

Solution conformation study of substance P methyl ester and [Nle10]-neurokinin A (4-10) by NMR spectroscopy

High-resolution proton spectra at 500 MHz of two tachykinin peptides, substance P methyl ester (SPOMe) and [Nle10]-neurokinin A (4-10), have been obtained in dimethylsulfoxide (DMSO), and for SPOMe, also in 2,2,2-trifluoroethanol (TFE)/water mixtures. Complete chemical shift assignments for these peptides were made based on two-dimensional (2D) nmr techniques, correlated spectroscopy and total COSY. J coupling measurement and nuclear Overhauser effect spectroscopy (NOESY) were then used to determine the conformation of these peptides in the various solvents. Based on the J coupling, NOE correlations, and temperature coefficients of the NH resonances, it is concluded that these two peptides exist in DMSO at room temperature as a mixture of conformers that are primarily extended. For SPOMe in TFE/water with high TFE content, however, helical structures are found to be present, and they become quite clear at temperatures between 270 and 280 K. The variation of the 13C chemical shifts of the C alpha (the secondary shift) with TFE contents corroborates this conclusion. The NOE and C alpha shifts show that the main helical region for SPOMe lies between 4P and 9G. The C-terminus segment L-M-NH2 is found to be quite flexible, which appears to be quite common for neurokinin-1 selective peptides.

The myotropic peptides of Locusta migratoria: structures, distribution, functions and receptors

The search for myotropic peptide molecules in the brain, corpora cardiaca, corpora allata suboesophageal ganglion complex of Locusta migratoria using a heterologous bioassay (the isolated hindgut of the cockroach, Leucophaea maderae) has been very rewarding. It has lead to the discovery of 21 novel biologically active neuropeptides. Six of the identified Locusta peptides show sequence homologies to vertebrate neuropeptides, such as gastrin/cholecystokinin and tachykinins. Some peptides, especially the ones belonging to the FXPRL amide family display pleiotropic effects. Many more myotropic peptides remain to be isolated and sequenced. Locusta migratoria has G-protein coupled receptors, which show homology to known mammalian receptors for amine and peptide neurotransmitters and/or hormones. Myotropic peptides are a diverse and widely distributed group of regulatory molecules in the animal kingdom. They are found in neuroendocrine systems of all animal groups investigated and can be recognized as important neurotransmitters and neuromodulators in the animal nervous system. Insects seem to make use of a large variety of peptides as neurotransmitters/neuromodulators in the central nervous system, in addition to the aminergic neurotransmitters. Furthermore quite a few of the myotropic peptides seem to have a function in peripheral neuromuscular synapses. The era in which insects were considered to be "lower animals" with a simple neuroendocrine system is definitely over. Neural tissues of insects contain a large number of biologically active peptides and these peptides may provide the specificity and complexity of intercellular communications in the nervous system.

Conformational study of two substance P hexapeptides by two-dimensional NMR

The conformation of two substance P (SP) related hexapeptides. Glp-Phe-Phe-(L-Pro)-Leu-Met.NH2 (I) and Glp-Phe-Phe-(D-Pro)-Leu-Met.NH2 (II), in two solvents, chloroform-d and trifluoroethanol(TFE)-d3/H2O, was studied by two-dimensional NMR methods, including COSY, TOCSY, ROESY and HMQC. The study shows that these two peptides exist predominantly in the extended form in TFE/H2O, but in general exhibit a reverse-turn structure in chloroform. I is clearly less ordered than II in both solvents. Furthermore, extensive Phe3-Pro4 cis<==>trans isomerization was found in I but not in II. The differences in the conformational behavior of these two peptides, which are selective agonists for neurokinin NK1 and NK2 receptors, respectively, are discussed.

Influence of the replacement of amino acid by its D-enantiomer in the sequence of substance P. 1. Binding and pharmacological data

The D-enantiomer of residues 2, 4, 5, 6, 7, 8, 10 and 11 was introduced in the sequence of Substance P: Arg-Pro-Lys-Pro-Gln-Gln-Phe-Phe-Gly-Leu-Met-NH2. The achiral glycine residue was replaced by a D-Ala residue. Regarding NK-1 binding potencies or activities, changing to the D-enantiomer in positions 2, 4 or 5 did not modify the pharmacological patterns of the resulting peptides. Introduction of a D-residue in the 6 to 11 sequence drastically decreased the potency of the D-analogues with the exception of [D-Leu10]SP which was found only three times less potent than SP in contracting the guinea-pig ileum. No clear cut evidence between the binding potencies and activities on NK-1, NK-2 and NK-3 assays, was observed which allows a more rational design of tachykinins antagonists.

Effects of tachykinins on [3H]taurine release from human astrocytoma cells (U-373 MG)

Substance P (SP) stimulated [3H]taurine release from human astrocytoma cells (U-373 MG). This effect was concentration dependent and the EC50 was 0.3 nM. This stimulatory effect of SP can be inhibited by spantide, a SP receptor antagonist. The rank order of potencies of related tachykinins and their analogues in stimulating the release of [3H]taurine was SP much greater than neurokinin A much greater than neurokinin B and [Glp6,L-Pro9]SP (6-11) much greater than [Glp6, D-Pro9]SP (6-11) which conformed to that reported for the tachykinin NK-1 receptor. In addition to SP, isoproterenol, a beta-adrenergic agonist, can also increase the release of [3H]taurine from these cells and the effects of SP and isoproterenol were additive.

The effects of neurokinin A, neurokinin B, and eledoisin on substance P analysis

Commercial sources for neuropeptide radioimmunoassays have made this sensitive tool available to clinical investigators for monitoring the potential involvement of neuropeptides in pain modulation. We measured substance P-like immunoreactivity in the plasma, saliva, and pericardial fluid of subjects with and without pain (chronic and acute) to determine if substance P levels are altered. Some recent studies have suggested that substance P in various body fluids may be a correlate of chronic pain. To test this correlation it is important to ensure that the assay is measuring what it was designed to measure. Therefore, the influence of three tachykinins on the analysis of substance P concentrations was assessed with a commercially available radioimmunoassay kit. A small (approximately 2 to 6%), apparently nonspecific elevation in measured substance P was found when alpha-neurokinin, beta-neurokinin, or eledoisin was incubated with substance P and its antibody. Our results also indicate an apparent specific affinity of the substance P antibody for alpha-neurokinin (above 1,000 pg/ml) and beta-neurokinin (above 5,000 pg/ml). Substance P levels in the body fluids we tested ranged from 0.47 to 62.88 pg/mg protein (47.4 to 230.8 pg/ml). Levels of the tested tachykinins have not been determined in body fluids. If alpha-neurokinin or beta-neurokinin is found to be present in high concentrations in these fluids, this commercially available substance P kit may overestimate substance P levels. The concentrations of tachykinins necessary to interfere specifically with the assay are 10- to 100-fold higher than substance P in body fluids.(ABSTRACT TRUNCATED AT 250 WORDS)

Locustatachykinin III and IV: two additional insect neuropeptides with homology to peptides of the vertebrate tachykinin family

Two myotropic peptides termed locustatachykinin III and IV were isolated from 9000 brain-corpora cardiaca-corpora allata-suboesophageal ganglion extracts of the locust, Locusta migratoria. The primary structures of Lom-TK III and IV were established as amidated decapeptides: Ala-Pro-Gln-Ala-Gly-Phe-Tyr-Gly-Val-Arg-NH2 (Lom-TK III) and Ala-Pro-Ser-Leu-Gly-Phe-His-Gly-Val-Arg-NH2 (Lom-TK IV). The locustatachykinins were synthesized and shown to have chromatographic and biological properties identical with those of the native materials. They stimulate visceral muscle contractions of the oviduct and the foregut of Locusta migratoria and of the hindgut of Leucophaea maderae. Both peptides exhibit sequence homologies with the vertebrate tachykinins. Sequence similarity is greater with the fish and amphibian tachykinins (up to 40%) than with the mammalian tachykinins. In addition, the intestinal and oviducal myotropic activity of the locustatachykinins is analogous to that of vertebrate tachykinins. Both chemical and biological similarities of vertebrate and insect tachykinins substantiates the evidence for a long evolutionary history of the tachykinin peptide family.

Locustatachykinin I and II, two novel insect neuropeptides with homology to peptides of the vertebrate tachykinin family

Two myotropic peptides termed locustatachykinin I (Gly-Pro-Ser-Gly-Phe-Tyr-Gly-Val-Arg-NH2) and locustatachykinin II (Ala-Pro-Leu-Ser-Gly-Phe-Tyr-Gly-Val-Arg-NH2) were isolated from brain-corpora cardiaca-corpora allata-suboesophageal ganglion extracts of the locust, Locusta migratoria. Both peptides exhibit sequence homologies with the vertebrate tachykinins. Sequence homology is greater with the fish and amphibian tachykinins (up to 45%) than with the mammalian tachykinins. In addition, the intestinal myotropic activity of the locustatachykinins is analogous to that of vertebrate tachykinins. The peptides discovered in this study may just be the first in a whole series of substances from arthropod species to be identified as tachykinin family peptides. Moreover, both chemical and biological similarities of vertebrate and insect tachykinins substantiate the evidence for a long evolutionary history of the tachykinin peptide family.

Reinforcing effects of peripherally administered substance P and its C-terminal sequence pGlu6-SP6-11 in the rat

Reinforcing effects of intraperitoneally (IP) administered substance P (SP1-11), its amino-terminal fragment SP1-7 (SPN) and an analog of the carboxy terminus (pGlu6-SP6-11: SPC) were studied in rats. Two conditioned place preference paradigms were used. After three pairings of the drug with a certain environment the effect of the treatment was evaluated in the drug-free state during a test trial. The reinforcing effects of SP (37 nmol) and the equimolar dose of SPC were expressed by a significant increase in the amount of time the animals spent in the treatment environment. Other doses of SP (3.7 and 185 nmol) and SPC (7.4 and 185 nmol) and none of the doses of SPN (37, 185, 370 nmol) influenced the place preference behavior of the rats. The reinforcing effects of SP parallel the known facilitating effects of peripherally administered SP on memory. The amino acids that encode the reinforcing effects of SP may lie within the C-terminal sequence of the SP molecule.